Maintaining correct inflation pressure in vehicle tires is accepted as an effective way to increase fuel economy, decrease tire wear and increase safety. Although proper tire inflation may be maintained by regularly checking tire pressure and adjusting accordingly, such maintenance tends to be largely ignored because of the inconvenience involved. Studies show that a tire will lose one to two psi of pressure per month in cool weather and more in warmer weather. Such resulting under-inflated tires not only cause fuel waste and excessive tire wear, estimated to cost over ten billion dollars annually in the United States alone, but also cause thousands of traffic accidents annually.
Prior art devices depending on tire deformation to move a piston and thereby activate a compressor located on a wheel generally transfer deformation motion directly to piston motion through rigid members, with larger deformations urging proportionately larger piston strokes. However, because an adequate compression ratio must be provided by a piston stroke for a slightly under-inflated tire that deforms only a fraction of an inch, an effective piston stroke must be provided by piston movement not exceeding a fraction of an inch. As is evident, when a tire is significantly under-inflated, direct coupling of deformation urges a piston movement far beyond its needed stroke length, thereby causing breakage of the rigid member or damage to the tire during each revolution as the rigid member bears the entire weight borne by the affected wheel-and-tire assembly.
In view of the economic and safety benefits of maintaining proper tire pressure, coupled with the general inconvenience of accomplishing such pressure maintenance and the inadequacies of prior art devices, it is apparent that a need is present for a dependable apparatus fully contained on a vehicle wheel or a portion thereof for maintaining proper inflation pressure within a mounted tire. Accordingly, a primary object of the present invention is to provide an automatic tire inflation device that is simple, inexpensive, practical and easy to install on an existing wheel.
Another object of the present invention is to provide a tire inflation device that can be added to existing wheels rather than requiring specially designed wheels for accommodation.
Yet another object of the present invention is to provide a tire inflation device wherein a valve stem also functions as an air inlet for inflation maintenance.
These and other objects of the present invention will become apparent throughout the description thereof which now follows.